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The protein–nanomaterial interface 总被引:1,自引:1,他引:0
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The effects of histamine on the activity of rapidly adapting receptors (RAR) of the airways were investigated in anesthetized dogs. With bolus injections given into the right atrium, the threshold dose of histamine required for the excitation of RAR (n = 7) was 0.82 microgram/kg (+1.33/-0.51, geometric mean). With increasing doses of histamine, a dose-response relationship was seen in the activity of RAR. Obstruction of the lymphatic drainage from the lungs reduced the threshold dose to histamine (i.e., shifted the dose-response curve to the left significantly). This change in the dose-response relationship was not accompanied by a corresponding change in the relationship of histamine dose to airway pressures recorded before and after lymphatic obstruction. Against a background of pulmonary venous congestion produced by partial obstruction of the mitral valve, subthreshold doses of histamine stimulated the RAR (n = 4). The excitatory effect of histamine on RAR was found to be abolished by the administration of the H1 receptor antagonist diphenhydramine but not by the H2 receptor antagonist cimetidine. Intravenous infusion of histamine (0.4 microgram.kg-1.min-1) for a period of 10 min increased the RAR activity (n = 6) significantly without producing detectable changes in airway mechanics. The results indicate that contraction of the smooth muscle of the airways may not be a prerequisite for the excitation of RAR, especially at low doses. It is suggested that some of the effects of histamine on RAR are mediated by a local expansion of the extravascular fluid caused by an increase in the permeability of the bronchial vasculature. 相似文献
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Chitin synthesis in third-instar Lucilia cuprina larvae cultured at 23 °C was investigated using in vivo and in vitro systems, the latter with whole and with homogenized integuments. Synthesis was at a maximum between 24 and 48h after ecdysis from the second instar. Chitin was deposited in layers, and labeled GlcNAc was rapidly cleared from the hemolymph. In in vitro homogenate systems, the rapid conversion of UDP-([14C]GlcN)Ac to ([14C]GlcN)Ac and its 1-phosphate derivative contributed to the low incorporation of this precursor into chitin. The extent of the conversion was reduced by the addition of KCN or phenylthiourea. In in vivo and in vitro tissue systems the level of incorporation of ([14C]ClcN)Ac was higher than that of UDP-([14C]GlcN)Ac. However, in in vitro homogenate systems there was no difference unless UTP was added when the level of incorporation of only ([14C]GlcN)Ac was increased (by a factor of 9). Incorporation of UDP-([14C]GlcN)Ac, but not that of ([14C]GlcN)Ac, was decreased when larvae were deprived of food. Soluble oligosaccharides were detected in in vitro homogenate systems. They were formed during chitin synthesis and may represent newly initiated chitin chains. A reappraisal of current ideas on chitin synthesis in insects is needed. 相似文献
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Simon C. Allen K. Ravi Acharya Kathleen A. Palmer Robert Shapiro Bert L. Vallee Harold A. Scheraga 《Journal of Protein Chemistry》1994,13(7):649-658
The three-dimensional structure of human angiogenin has been determined by X-ray crystallography and is compared here with an earlier model which predicted its structure, based on the homology of angiogenin with bovine pancreatic ribonuclease A. Comparison of the predicted model and crystal structure shows that the active-site histidine residues and the core of the angiogenin molecule, including most of the-strands and-helices, were predicted reasonably well. However, the structure of the surface loop regions and residues near the truncated C-terminus differs significantly. The C-terminal segment includes the active-site residues Asp-116, Gln-117, and Ser-118; Gln-117 in particular has been shown to be important in affecting the ribonucleolytic activity of angiogenin. Also, the orientation of one helix in the model differed from the orientation observed experimentally by about 20°, resulting in a large displacement of this chain segment. The difficulty encountered in predicting the surface loop regions has led to a new algorithm [Palmer and Scheraga (1991),J. Comput. Chem.,12, 505–526; (1992),J. Comput. Chem.,13, 329–350] for predicting the conformations of surface loops. 相似文献
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Sixth instar Choristoneura occidentalis Freeman and 5th instar Orgyia pseudotsugata (McDunnough) were fed ring-labelled 14C-diflubenzuron coated on Douglas-fir needles. After ingestion the gut was purged of radioactive needle residues with artificial diet. Radioactivity in body and frass extracts and residues were measured. Diflubenzuron in extracts were separated from metabolites by thin layer chromatography.Ninety percent and 86% of the ingested diflubenzuron passed through the body without being absorbed in C. occidentalis and O. pseudotsugata, respectively. Bodies of C. occidentalis retained 0.3% of ingested diflubenzuron, while O. pseudotsugata retained 5.3%. This difference in % diflubenzuron retention in the body was negatively correlated with % relative metabolism in the two species. Relative toxicities of diflubenzuron to the two species may be related to % retained diflubenzuron which may be due to a significant difference in relative metabolism.
Zusammenfassung Sechstraupen von Choristoneura occidentalis Freeman und Fünftraupen von Orgyia pseudotsugata (McDunnough) wurden Douglasiennadeln gefüttert, die mit ringmarkiertem 14C-Diflubenzuron überzogen waren. Nach der Nahrungsaufnahme wurde der Darm von radioaktiven Nadelresten befreit durch Fütterung einer künstlichen Diät. Die Radioaktivität der Körper- und der Kotextrakte und der Nahrungsreste wurde gemessen. In den Extrakten wurde durch Dünnschichtchromatographie Diflubenzuron von den Metaboliten getrennt.90% resp. 86% des aufgenommenen Diflubenzuron ging durch den Körper hindurch, ohne von den Raupen von C. occidentalis und O. pseudotsugata aufgenommen zu werden. Der Körper von C. occidentalis behielt 0.3%, derjenige von O. pseudotsugata 5.3% des aufgenommenen Diflubenzurons zurück. Dieser Unterschied im prozentualen Zurückhalten von Diflubenzuron war negativ korreliert mit dem prozentualen Metabolismus in beiden Arten. Die relative Giftigkeit von Diflubenzuron auf beide Arten mag abhängig sein vom Prozentsatz zurückgehaltenen Wirkstoffs. Dieser dürfte abhängig sein vom wesentlich unterschiedlichen Ausmass des Metabolismus.相似文献
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3β-hydroxy-5-cholenoic acid was found in the bile and feces of new-born and fetal guinea pigs. The identity of this compound was confirmed by gas chromatography and mass spectrometry. This finding suggests that the formation of chenodeoxycholic acid through 3β-hydroxy-5-cholenoic acid is intermediate in the early life of guinea pigs. Thus, it provides a useful model for studying the details of regulatory factors and significance of this pathway. This study also revealed that, unlike the adult guinea pig, the newborn guinea pig has significant amounts of glycine conjugates of bile acid. 相似文献